Summary of Significant Accounting Policies - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Basic EPS
Net income attributable to common stockholders	$ 40,421	$ 35,063	$ 80,665	$ 79,725
Weighted-Average Shares (in shares)	10,833,000	10,796,000	10,817,000	10,782,000
Basic EPS (in dollars per share)	$ 3.73	$ 3.25	$ 7.46	$ 7.40
Effect of dilutive securities
SARs and restricted stock (in shares)	83,000	68,000	100,000	94,000
SARs and restricted stock (in dollars per share)	$ (0.03)	$ (0.02)	$ (0.07)	$ (0.07)
Net income, Diluted EPS	$ 40,421	$ 35,063	$ 80,665	$ 79,725
Weighted-Average Shares, Diluted EPS (in shares)	10,916,000	10,864,000	10,917,000	10,876,000
Diluted EPS (in dollars per share)	$ 3.70	$ 3.23	$ 7.39	$ 7.33
Stock Appreciation Rights and Restricted Stock
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	34,500	42,922	48,605	46,464
Performance Shares
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	32,282	18,535	32,282	18,535